1. Field of the Invention
The present invention relates generally to the field of solenoid valves, and, more particularly, to an improved pulse-width-modulated (PWM) solenoid valve having a long service life.
2. Description of the Prior Art
Solenoid valves are, of course, well known. Generally, these valves have a poppet member mounted within a body for movement toward and away from a fixed seat. An armature is normally connected to the poppet member. The poppet member is typically biased to move to a closed position by a return spring. However, it has been Applicant's experience that such solenoid valves do not have a long life when controlled by a pulse-width-modulated technique, wherein the solenoid valve is typically opened and closed two or three hundred times each second. One reason for limited life is that the combined mass of the armature and poppet impacts repeatedly against the seat, causing deformation which adversely affects valve leakage and flow characteristics. This is believed to substantially shorten the operating life of the valve. Other details of prior art PWM solenoid valves are shown and described in Technical Bulletin 151, "Electropneumatic Servoactuation: An Alternative to Hydraulics for Some Low Power Applications", Moog Inc. (1984).